Zinc is known to play a central role in the immune system. For zinc-deficient persons they are likely to experience increased susceptibility to a variety of pathogens.
Zinc has a primary role in the gene regulation within lymphocytes and is crucial for normal development and function of cells mediating non-specific immunity such as neutrophils and natural killer cells.

The macrophage, an essential cell in many immunologic functions, is adversely affected by zinc deficiency, which can dysregulate intracellular killing, cytokine production, and phagocytosis. Cytokines are important proteins secreted by many types of cells when the immune system is faced with inflammatory and infectious diseases. They have synergistic immune effects when bound with antibodies.

Zinc also functions as an antioxidant and can stabilize membranes. Therefore, free radicals can be picked up and brought away from cells and as a result cells do not get oxidised and lysed. Zinc deficiency also affects development of acquired immunity by preventing both the outgrowth and certain functions of T lymphocytes such as activation and Th1 cytokine production. Likewise, B lymphocyte development and antibody production, particularly immunoglobulin G, is compromised.

In addition, Zinc is also a cofactor in more than 300 enzymes influencing various organ functions, therby having a secondary effect on the immune system.

In general, all kinds of immune cells show decreased function after zinc depletion. In monocytes, all functions are impaired, whereas in natural killer cells, cytotoxicity is decreased, and in neutrophil granulocytes, phagocytosis is reduced.

BEWARE!

Excessive intake of zinc can impair immune responses too. From the Journal of the American Medical Asscoiation, a study was carried out on eleven healthy adult men. They were required to ingest 150 mg of elemental zinc twice a day for six weeks. It was then observed that the serum high-density lipoprotein concentration decreased significantly and low-density lipoprotein level increased slightly. This was associated with a reduction in lymphocyte stimulation response to phytohemagglutinin as well as chemotaxis and phagocytosis of bacteria by polymorphonuclear leukocytes. Thus, zinc supplementation on an excessive intake could have adverse effects in healthy persons.

Many thanks to:
The American Society for Clinical Nutrition,Inc
American Medical Association

Both sources are retrieved on 9 February 2007.